This extension adds a test wiki system originally designed for the Wikimedia Incubator. It can also be adapted to be used for wiki virtualization, i.e. wikis inside the real wiki. Each virtual wiki (aka test wiki) is linked to a project (e.g. Wikipedia) and a language, which form the prefix for a page (Wx/xyz).

A brief overview of the features:

A preference where you can enter the test wiki you are working on

A special page "Special:ViewUserLang" to view the language and test wiki preference of a user

The extension is configured by default for the Wikimedia Incubator. With some configuration changes, it may also work for other wikis using a "virtual wiki" system. These are general configuration settings; specific settings can be found in the section "Features".

The project codes with their names. The extension might break if you use more than one letter for the code.

On Special:Preferences, beneath the language selector, you can select the test wiki you are working on. You can select the project (Wikipedia, Wikibooks, ...) and the language code. It defaults to "None/All". Another option, "Maintenance" is intended for users, mostly administrators, who do maintenance and are not working on a test wiki.

A magic word "{{USERTESTWIKI}}" which displays the prefix depending on the value you selected. Using &testwiki=wx/xyz in the URL should alter this value in principle, but this is not reflected on the page due to the cache. In general, &testwiki=wx/xyz works in a similar way as &uselang=xx, respectively for the test wiki and language preference.

The name of the preference (not really important, shouldn't be changed):

A special pages, Special:ViewUserLang is added where users with the 'viewuserlang' right, can view the interface language and selected test wiki of a user. This can be useful information when a user has a problem with the test wiki system.

Special:MyMainPage redirects you to the Main Page of the test wiki that you selected, i.e. "Wx/xyz?goto=mainpage" (see section "Info pages"). If no preference selected or "Incubator" is selected, you are redirected to the regular Main Page.

Special:RandomByTest redirects you to a random page in your test wiki. If &testwiki=wx/xyz is specified in the URL, it will redirect you to a random page in that test wiki. If your preference is set to "Incubator" it behaves like Special:Random below version 1.18; or goes to a random help or project page in 1.18 and above.

Special:SearchWiki allows to find an existing wiki as well as test wikis. You can select the project you are looking for, and the language name or language code. It will redirect automatically if the wiki is found. The special page can be transcluded on normal pages.

Special:IncubatorFirstSteps guides the user through setting up his account, his test wiki preference and starting a test wiki.

The recent changes special page is adapted to display the edits in the test wiki of your preference. "None/All" returns the normal display, and "Incubator" displays all edits that are not made in a test wiki. You can select the project and enter a language code to view the recent changes of a specific test wiki, or you can use &testwiki=wx/xyz in the URL.

On root "Wx/xyz" pages, a placeholder is shown if that page does not exist (following redlinks redirects you to viewing the page instead of editing it). For non-existing wikis, it shows a welcome page and invites the user to start a test wiki in this language and project. There are also links to sister projects and multilingual projects, according to the configuration.

The project URLs and names of multilingual projects, i.e. related projects for which there are no translated versions and thus no test wikis.

If the URL includes &goto=mainpage, it redirects to to the existing subdomain in case that exists; otherwise it redirects you to a subpage "Wx/xyz/Main Page" where "Main Page" is translated depending on the MediaWiki localisation of the language of that test wiki.

Pseudo-category namespaces, e.g. "Category:Maintenance:Delete". Creating unprefixed pages in category namespaces is restricted by default, but for some categories related to the site itself, it is useful to allow creating subcategories. It only allows colons (:) as delimiter. (See incubator:Category:Users:By_language as an example.)

Pages belonging to test wikis that have an existing subdomain, cannot be edited nor created and display a message linking to the existing wiki. If your test wiki preference is set to that test wiki, or if &testwiki=wx/xyz equals to that test wiki, you are redirected to the wiki.

Pages in test wiki namespaces, that lack a prefix, cannot be created (but existing unprefixed pages can be edited). It shows an error message, and if you have set a test wiki preference, it suggests to create a correctly prefixed page.

Pages in test wiki namespaces are marked as being written in the language depending on the "xyz" language code. This means for example that pages of "Wx/ar" (Arabic) and "Wx/he" (Hebrew) are from right-to-left.

If your preference or &testwiki=wx/xyz is set to the test wiki you are viewing, the logo changes to the image specified in MediaWiki:Incubator-logo-wx-xx if available (where Incubator is the name set in $wmincProjectSite), and otherwise MediaWiki:Wminc-logo-project (where project is the name as in $wmincProjects).

Configuration is set by default to create a user group of "test administrators", who have limited administrator rights like delete, undelete, view deleted history, block, block email and rollback. There is no technical restriction (yet) that a test admin can only perform actions within his/her test wiki.

Special:ListUsers can be filtered by test wiki. You can input a test wiki prefix ("Wx/xyz") or "Incubator" and it will filter the list of users to those who have set their test wiki preference to that.

You can search in a test wiki if the search engine supports it (which is true on WMF wikis). It will do so by default in your test wiki, but you can change it by using the input form that is shown in the advanced search form.

Also, a custom message will be shown, either "Set your test wiki preference so we can tell you which page to create!" or "You can create Wx/xyz/Search_term!".

This extension is being used on one or more Wikimedia projects. This probably means that the extension is stable and works well enough to be used by such high-traffic websites. Look for this extension's name in Wikimedia's CommonSettings.php and InitialiseSettings.php configuration files to see where it's installed. A full list of the extensions installed on a particular wiki can be seen on the wiki's Special:Version page.